1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device. Specifically, the present invention relates to a method for manufacturing a semiconductor device after grinding the back surface of the semiconductor substrate when forming a through-substrate (-silicon) via (hereinafter referred to as “TSV”) penetrating the semiconductor substrate. Also, the present invention relates to a method for manufacturing a semiconductor device comprising a TSV.
2. Description of the Related Art
In order to meet demands for miniaturizing semiconductor devices, technology wherein a plurality of semiconductor chips is stacked and TSVs are provided to connect the semiconductor chips has been developed. There is a method for forming a TSV comprising: forming a deep hole on the main surface where semiconductor elements are formed; filling a conductive film in the hole; and exposing the conductive film by grinding the back surface of the semiconductor film. Another method comprises: grinding the back surface of a semiconductor substrate, on the main surface of which semiconductor elements are formed; forming a through hole; and filling a conductor into the through hole. The latter method allows the thickness of a semiconductor substrate to become between 10 and 100 μm, thereby easily processing the semiconductor substrate. Also, it allows a semiconductor chip to become thinner, thereby miniaturizing the semiconductor device when stacking semiconductor chips.
When making the back surface of a semiconductor substrate, on the main surface of which semiconductor elements are formed, thinner by grinding it, in order to protect the semiconductor elements on the main surface or to prevent the semiconductor substrate from being broken, it is general to fix a support (support substrate), such as quartz, etc., onto the main surface of the semiconductor substrate by use of an adhesive (JP 2007-311385A).
When forming a TSV on the main surface of a semiconductor substrate, on which semiconductor elements are formed, in order to connect a terminal, etc. for easier external connection to the TSV, a wiring layer or a conductive pad is formed after grinding the back surface. Also, when forming a TSV on the back surface, the TSV is formed after grinding the back surface, and a wiring layer or a conductive pad may be formed on the back surface. Such conductive films are formed while fixing a support to hold the main surface of the semiconductor substrate. Along with the adhesive, the support is removed from the semiconductor substrate after forming the conductive films.
The inventor of the present invention discovered that a process for manufacturing a conductive film including a TSV after grinding the back surface of a semiconductor substrate, to which a support is fixed, has the following problems.
FIGS. 10 to 13 are prepared by the present inventor in order to explain the problems of the conventional process for manufacturing a conductive film.
FIG. 10 is a sectional view of a semiconductor substrate (wafer) to which a support is fixed, and FIG. 11 is a plane view thereof. As shown in FIGS. 10 and 11, semiconductor substrate 1, such as silicone (Si), etc., is fixed to support 2, such as quartz, etc., by use of adhesive 3, such as a photocurable resin, etc. Both semiconductor substrate 1 and support 2 are circular substrates in plane. Support 2 has a diameter slightly greater than that of semiconductor substrate 1.
Semiconductor substrate 1 is fixed in the direction where a main surface S, on which a circuit layer comprising a plurality of semiconductor elements, i.e., transistor, etc., is formed, faces support 2. In other words, as shown in FIG. 10, semiconductor substrate 1 is fixed such that the back surface thereof is upward. When fixing semiconductor substrate 1 to support 2, adhesive 3 applied in the liquid state is flown out from the side of semiconductor substrate 1. Thus, as shown in FIG. 10, the side of semiconductor substrate 1 is also covered with adhesive 3.
After curing adhesive 3, the back surface (upper surface in FIG. 10) of semiconductor substrate 1 is ground (back-ground), so that semiconductor substrate 1 is adjusted to have a predetermined thickness. FIG. 12 is an enlarged view of the end (portion indicated by broken lines in FIG. 10) of semiconductor substrate 1 after performing such processes.
The adhesive contracts due to mechanical stress caused by the grinding of semiconductor substrate 1, slight bending of support 2, or heat generated by plasma etching, etc. after the grinding of semiconductor substrate 1. As a result, gap d0 of several μm is made between semiconductor substrate 1 and adhesive 3. Gap d0 may be made in the entire or a part of the outer periphery of semiconductor substrate 1.
When gap d0 is made as shown in FIG. 12, if the TSV is processed (forming a conductive film) by use of a sputtering device, the surface of adhesive 3, which is an insulator, is charged-up and, thus, the local electric potential is likely to be increased. Local electric potential is not likely to be increased in the semiconductor substrate, because semiconductor substrate 1 is a silicon layer and charge is quickly moved over the entire of semiconductor substrate 1. Therefore, when the surface of adhesive 3 has electric potential greater than predetermined electric potential, thus over potential is discharged to semiconductor substrate 1, as shown in FIG. 13. Generally, before forming a conductive film and after grinding the back surface, an insulating film is formed. However, even though such insulating film is provided, thus discharge phenomenon takes place if the insulating film is thinner at sub-micron order. Since a large current instantaneously flows along with discharge, a current path on the semiconductor substrate is damaged (the substrate is hollowed-out). As a result, it is not possible to successfully process semiconductor layers, such as a TSV, etc.
As mentioned above, the conventional manufacturing method has a problem that the production yield of semiconductor devices is likely to be reduced due to discharge.